Genetic damage appears to lie at the heart of tumorigenesis. The damage is of two sorts: dominant, with targets known as proto-oncogenes; and recessive, with targets known as tumor suppressor genes. The work supported by this grant seeks the identity of the damaged genes, their contributions to tumorigenesis, the biochemical mechanisms by which they act, and their roles in the normal cell and organism. Success with these objectives might provide new and more rational strategies for the prevention, diagnosis and therapy of cancer; and it should also reveal principles by which the normal proliferation and differentiation of cells are controlled. The search for additional cancer genes will be conducted in cell culture and transgenic mice, using in particular new strategies for the detection of tumor suppressor genes, with special attention to the distinctive steps in tumor progression, and with a focus on neurological tumors and leukemia. The cancer genes identified to date act by one of three means: protein phosphorylation, signalling by GTPase's, and control of transcription. Each of these will be studied, with emphasis on where they act and how they are controlled in normal cells, how they are integrated into the signalling pathways of the cell, how they figure in cellular proliferation or differentiation, how they serve during organismal development, and how they can contribute to neoplastic transformation. Most attention will be given to the protein-tyrosine kinases encoded by the proto-oncogenes SRC and HCK, and the transcription factors encoded by MYB and MYC. But the products of HRAS, the tumor suppressor genes RB and P53, and the E7 oncogene of Human Papilloma Virus will also be studied. The work will rely on diverse experimental methods, including: molecular cloning, DNA-mediated gene-transfer, retroviral vectors, immunochemistry, biochemical analysis in vitro, site-directed mutagenesis of recombinant DNA, nucleotide sequencing, protein purification, specialized cell culture, molecular screening procedures in yeast, genes made conditional by placing the activity of their protein products under the control of asteroid hormone, genetic analysis in Drosophila melanogaster, and manipulation of genes in mice by homologous recombination - all designed to identify the normal functions of genes in a developing organism and to map the signalling pathways by which these functions are executed.